1. Field of the Invention
This invention is related to valves and more particular to pinch-type valves.
2. Background Information
Pinch valves are used desirably for controlling flow of fluids in a variety of processes and environments. In general, a pinch valve is a mechanism that provides a variable-diameter pinching force to a flexible or elastomeric tube/hose. By pinching, or constricting the tube, the amount of flow therethrough is reduced from full, unrestricted flow, or completely shut off. One advantage of pinch valves is that the actuating mechanism is located outside of the tube interior lumen. The fluid never confronts any gates, flaps or other jointed/seamed parts. Rather, the fluid only confronts the pinched (but otherwise unbroken) inner wall of the tube. This greatly reduces the chances of undesirable accretion of particulates in multiphase or colloidal mixtures. In a conventional, gated valve with cracks, seams or discontinuities, such accretions are much more likely to occur.
In medical applications small-scale pinch valves are used frequently for regulating the flow of gasses and vital fluid, especially those containing particulates, such as whole blood. In general, larger-diameter flow conduits used in chemical processing may also use pinch valves where particulate accretion may be a concern.
A prior art pinch valve is described in U.S. Pat. No. 4,682,755 entitled MECHANICAL CONTROL SYSTEM IN FLOW DEVICES, by Bernstein, et al. This patent teaches a pinch valve structure in which a pair of same-direction-rotating eccentric pinch members move toward and away from each other to regulate the size of a tube opening placed between them.
One disadvantage to a pinch valve of this and other types is that they tend to plastically deform and flatten the tube over time. Hence, when the pinch valve is moved from a highly constricted, to a more, fully open position, the tube may remain deformed in a more-constricted state. Where the internal pressure of the fluid is low, the flow may be undesirably restricted, due to the permanent deformation of the tube.